There are various circumstances in the health care field where it is desirable to measure some physiological characteristic of a subject person and it is convenient to make such measurement using a sensor which interfaces to the subject's ear.
For example, some known pulse oximetry sensors clip to a subject's earlobe. An example of one such pulse oximetry sensor is described in Bukta, U.S. Pat. No. 5,611,337. An example of a heart rate sensor which clips onto a subject's earlobe is shown in FIG. 3 of Greubel et al., U.S. Pat. No. 5,237,997. Various types of sensors may be clipped to a subject's earlobe. The output signals of such sensors may be used for various purposes including measuring heart rate, measuring blood oxygen saturation, measuring blood pressure, measuring temperature, or the like.
Clipping a sensor to a subject's earlobe is convenient. However, the inventors have identified a number of disadvantages of current earlobe sensors. These include the following:    Some sensors work best when located in a specific position on a subject's earlobe. A typical ear sensor can be clipped onto a subject's ear in different locations. It can be difficult to repeatedly find the position in which such a sensor works best. In some cases, it is necessary to try several times before a satisfactory output signal can be obtained.    Earlobe clips can be pulled off with relative ease.    Current earlobe sensors do not always stay fixed on a subject's ear but may move over time relative to a desired sensing location. This can cause the quality and fidelity of the sensor output signals to vary over time. Movements of the sensors may themselves create artifacts in the sensor output signals, further degrading output signal quality and fidelity.
Some sensors are designed to be inserted into a subject's ear canal. Thorgersen, U.S. Pat. No. 6,080,110 describes such a sensor. Such sensors have the disadvantages that they occlude the subject's ear canal and can be uncomfortable if kept in place for too long.
There is a need for ear sensors which ameliorate at least some of the disadvantages of current ear sensors. There is a particular need for ear sensors capable of generating quality, robust and stable pulse signals at a subject's ear.